1. Field of the Invention
This invention relates to packaging machines incorporating conveyor apparatus and particularly to packaging machines used for packaging of products in film wrap.
2. Description of the Related Art
A commonly used method of packaging items for sale involves wrapping the item in a sheet of film and sealing the film around the item. This method has been commercially employed for the packaging of food items, such as, for example, poultry products. In many industrial horizontal packaging machines, the poultry product is fed into a longitudinally sealed tube formed of the film wrap and then the tube is sealed transversely ahead of and behind the poultry product. This sealing is typically done by thermal or ultrasonic welding techniques using sealing bars.
As wrapping equipment has been made to operate faster, it has become necessary to modify the manner of conveying the poultry product, frequently transported in a tray, in order to maintain film control of the product during packaging and also during weighing and labelling operations. One means of improving the control comprises the use of vertical conveyor belts placed so as to engage opposite sides of the tray to enhance the synchronization of the product tray motion with the machine motions. See, for example, U.S. Pat. No. 5,137,099 with respect to use of vertical control belts in a weighing and labelling operation.
In order to improve the process speed and to maintain reliable film seals, there has been developed a mechanism able to cause the sealing bars which form the transverse seals to travel along with the film, and thus increase the seal cycle time. Such a mechanism is disclosed in Japanese patent application No. 4,121,444 for Packaging Machine Seal Mechanism and Control by Suga filed Apr. 15, 1992, the contents of which are deemed incorporated herein by reference.
In addition to the inherent problems associated with handling trays of poultry at high production speeds, the air within the wrapper is often evacuated so that a minimum of air is available within the wrap. This reduced quantity of air retards the natural degradation of the poultry, thus preserving it in useful condition for a longer time. However, the vacuuming needed to remove the air is powerful and rapid, and tends to pull the poultry toward the vacuum source. Since the most effective time to apply this vacuum is at the last instant before completing sealing of the package, the vacuum attempts to pull the poultry product from the partially sealed package.
In applicant's copending application Ser. No. 07/967,403 filed Oct. 28, 1992 entitled "BELT CONVEYOR PROVIDING A CONTROLLABLE LENGTH OF BELTRUM", and in a copending continuation-in-part thereof, Ser. No. 08/046,012 filed Apr. 12, 1993 entitled "PACKAGING MACHINE HAVING A CONVEYOR OF CONTROLLABLE LENGTH", there is provided a conveyor system having a reciprocable frame and suited to use in a packaging machine. The reciprocable frame mounts a horizontal conveyor belt, a pair of vertical control belts, or both, upstream of the sealing mechanism. The belts are normally in continuous rotation. When the frame reciprocates, the length of belt contacting the product lengthens and shortens and in doing so provides an effective means for firmly gripping and conveying the product upstream of the sealing head mechanism and to and through the sealing head mechanism. However, there remains a need for an improved packaging machine having a conveyor belt system capable of firmly gripping and conveying the product downstream from the sealing mechanism.
It is therefore an object of this invention to provide an improved packaging machine having a conveyor apparatus capable of controlling a product while being transported through the packaging machine particularly when being transported downstream from the sealing mechanism.
It is an additional object of this invention to provide a packaging machine having an improved conveyor apparatus to control a product being transported while being packaged and during application of a vacuum to exhaust air from within the package being formed.
Other objects and advantages will be more fully apparent from the following disclosure and appended claims.